This is an indication that the PLAN is transforming from a deterance force to presence force. As stated in its latest defence white paper, the main tasks of PLAN is "near seas defense and far seas protection". My understanding on the breakdown is:So much surface warship development. What's PLAN doing about its relative weakness below the surface? Anti-sub may have improved a lot and caught up if not surpassed but can they ensure any decent safety against the hordes of USN subs? They must be feeling pretty damn confident with PLAN's current anti-sub warfare but maybe this area doesn't get any attention or leaks from the authorities for a reason. Once you can detect subs with certainty and effectiveness, they are basically sitting ducks. In this respect, it is only a question of technology. The rest of the problem is securing airspace for anti-sub aircraft to release their ordinance. Could that be why China seems to consider air domain to be more important?
China's own sub fleet is a threat to the USN surface vessels more than they are to USN subs. It may not need the same level and numbers of submarines (though that's certainly useful for A2AD) to be totally capable of removing the USN submarine threat. It just seems while plenty of things are leaked and even very publicly shown and talked about, anti-sub insight is limited to just a few special mission aircraft and whispers of revolutionary detection tech. Anyway it's certainly true that if PLAN possess one or some new and effective anti-sub capabilities, it's only a matter of contesting and fighting for airspace - which explain spamming Type 055s and weapons dedicated to taking carriers.